I'm assuming that, in each case, the property in question was your PPR and not an investment. FTB rates of TRS apply for the first 7 years. If you switch mortgages or PPRs then, as far as I know (having been corrected here on AAM a while back), you still qualify for the FTB rate for what remains of your 7 year period. I presume that you get the Budget 2007 new rates for the remainder of your FTB 7 year period.
I'm going on a personal view of the (Revenue) information, not a deep knowledge so not a definitive answer.
1) If they are assessed as individuals (give up any gains from transfer of credits) they can definatly claim the remainder of the FTB relief for both.
2) Not 100%, but I would presume for year 1 of the new purchase they could be jointly assessed (gaining any transfers) and still recieve TRS at FTB levels.
If the seperate assessment is not going to change income then 2) is a mute point. For 1) worth checking that a tranfer of credits (jointly assessed) isn't worth more than the FTB TRS.
You have 7 years at the TRS FTB level. You can buy/sell as often as you like. It's a term, nothing to do with individual properties.
Edit: Looking at the above reply by CM thought it worth including, the new TRS levels etc. are only available where the property is your PPR and you retain OO status. The answers given relate to where TRS is definatly available and is in relation to the level of TRS, it is not dealing with issues of where TRS can/should be claimed.
Jump onto the Revenue site and a special form for backdating a claim. May be different when you just want to upgrade the level of payment so might be worth calling them to confirm if it's the same form.
I believe the four year rule still applies so act as soon as you can.